1. Field of the Invention
The present invention relates to a recording/reproducing system using an optical disk or a magneto-optical disk. In particular the invention relates to an optical disk system for recording information about start positions of plurality of block record data recorded in a user's recording area of a magneto-optical disk and information about linking and end positions of plurality of small-block record data constituting the block record data in an area other than the user's recording area of the magneto-optical disk.
2. Related Art
A compact disk (hereafter referred to as a CD) is hitherto known which is generally used as a medium for reproducing music signals. Recently, the research of a recording material of an optical disk medium has advanced, a recordable optical disk has been developed, and an apparatus for recording on a disk which has the same data format as the prerecorded CD has become practically usable. These recordable optical disks include a DRAW (Direct Read After Write)-type optical disks in which data can be recorded only once by deforming or vaporizing a recording material with the heat produced due to irradiation with a laser beam to form a recording pits. However, recorded data cannot be erased in this type of disk. These disks include an erasable-DRAW-type magneto-optical disk in which information can be repeatedly recorded and erased by using a laser beam as a light source and applying an external magnetic field to the magneto-optical disk from the side opposite to the light source to change the direction of perpendicular magnetization of a recording film. These magneto-optical disks are already practically used as an external memory unit of a computer.
Data in these magneto-optical disks is erased by applying a magnetic field reverse to that for recording to a recording film while irradiating a laser beam to the film and heating it. When the data in the magneto-optical disk is reproduced, a magneto-optical phenomenon called the Kerr effect is used to read the direction of magnetization. When applying a linearly-polarized laser beam to a perpendicular-magnetized film, the plane of polarization of reflected light slightly rotates counterclockwise or clockwise in accordance with the direction of magnetization. Information is reproduced by converting the rotation of the plane of polarization into a change of luminous energy using an analyzer.
As the method to record data in or erase data from the above magneto-optical disk, a light modulation method is used in which the data is recorded or erased by generating an N- or S-pole magnetic field at the side opposite to a laser beam centering around the magneto-optical disk and changing the laser power to a higher power by using a high-power laser when forming a mark and outputting a lower power similarly to a reproductive power when forming no mark to modulate the emitted laser power. In this case, the generated magnetic field supplementarily functions for recording. Also, in this case, it is impossible to overwrite the already recorded data.
However, though the operation theory is the same, an optical carrier recorder is being practically used in which a laser beam is emitted at a constant power from either side of a magneto-optical disk to record data by reversing the N and S poles of a magnetic field inversely to the case of the light modulation method. This is called the magnetic field modulation recording method in which already recorded data can be overwritten by modulating and recording a magnetic field. In the case of this method, it is possible to directly overwrite already recorded data without spending the time to erase the already recorded data and then recording new data.
For the above optical disk recorder conforming to the magneto-optical modulation recording method, a magneto-optical disk has recently been proposed which has the sampling frequency of 44.1 KHz and the resolution of 16 bits for two channels at a reproduction level similarly to current CD by using audio data compression/extension techniques. In this method, the information content to be recorded and reproduced is compressed up to 1/5, signals are recorded in an optical disk or magneto-optical disk, and the information read out for reproduction is extended to realize the similar audio performance as a CD.
This method has the following main specifications: the disk diameter is 64 mm, the track pitch is 1.6 .mu.m, audio data can be recorded or reproduced for up to 74 min, and the linear velocity of the disk is 1.2 to 1.4 m/sec. As to the audio signal performance, two stereo channels are used, the frequency band ranges from 5 to 20 KHz, the dynamic range is 105 dB, and the magnetic field modulation method as described above is used as the recording method. Moreover, in the case of the signal format, the sampling frequency is 44.1 KHz, EFM (Eight to Fourteen Modulation) the same as that of a CD is used as the modulation method, and CIRC (Cross Interleave Reed-Solomon Code) is used as the error correction method.
Furthermore, ATRAC (Adaptive Transform Acoustic Coding) is used as the high-performance coding method. This method demarcates analog-digital-converted audio data with a time frame of 11.6 msec, divides the data into a plurality of frequency bands by means of a MDCT (Modified Discrete Cosine Transform) operation to convert them into frequency axes by MDCT and thereafter decrease the quantity of the data by using the acoustic sense of a person to compress them up to the data quantity of approx. 1/5. Therefore, though the recording density of the magneto-optical disk is the same as that of a CD, it is possible to decrease the disk diameter necessary to record/regenerate data for up to 74 min. to 64 mm which is much smaller than that of the CD.
The following is the result of studying major features of the above optical disk recorder. To reproduce data from a CD, the CD has to continuously send signals of 1.4 Mbit/sec to a digital-analog converter (DAC). Therefore, reproduced signals must be read out of the CD in real time. In the case of a recorder using the data compression/extension technique, because the quantity of the data is compressed to approx. 1/5, 0.3 Mbits/sec is enough to decode a signal read out at the rate of 1.4 Mbits/sec since it is a compressed signal. Therefore, it is only necessary to intermittently read signals from the disk.
Thus, by storing signals read out of an optical disk in a storage circuit such as a buffer memory, it is possible to reproduce all the audio signals stored in the storage circuit. Therefore, if the tracing of an optical pickup is deviated from the original position due to vibrations of the optical disk recorder, out-put of second would be interrupted in the case of a CD but sound interruption does not occur in the case of the storage circuit storing data while the optical pickup recovers from the trouble. The interruption out-put of second does not occur as the optical pick-up returns to the original position on the optical disk and continuously reads signals while data is read out of the storage circuit and continuously reproduced.
By using the above storage circuit and data compression/extension techniques, another major feature is obtained. In the case of a CD, one piece of music, that is, track is always formed in consecutive areas on an optical disk as a group. However, in the case of the above magneto-optical disk system, one piece of music (tracks) can be formed even by dividing and recording plurality of block record data in random areas on an optical disk. This is because there is an idle time since the transfer rate necessary to decode a compressed signal is 0.3 Mbits/sec though signals are read out of the optical disk at the transfer rate of 1.4 Mbits/sec. Therefore, audio signals can be continuously outputted by reading signals out of the optical disk during the idle time and store them in the storage circuit, and thereafter moving the optical pickup up to a remote area on the optical disk (the block record data next to the track comprising separate plurality of block record data) to read signals out of the optical disk and storing them in the storage circuit before the storage circuit becomes empty.
Similarly, the same piece of music (tracks) can be continuously reproduced even if continuous audio signals are recorded in separate areas on the optical disk. The state showing that one track comprises a plurality of small-block record data (a plurality of record data in a recording block comprising continuous areas are separately present on an optical disk) is entered at a predetermined position of the optical disk as table-of-contents information. Therefore, to change the number of pieces of music or to perform editing such as dividing of a piece of music into two pieces of music, a waiting time is produced for the actual elapsed time of a position to be changed. In the case of the optical disk recorder, however, it is possible to easily change numbers by rewriting the composition information (linking information) of a piece of music in a certain area with the above table-of-contents information. Therefore, for editing, a major advantage is obtained by using the data compression/extension technique.
As described above, in the case of a magneto-optical disk recorder (hereafter referred to as MD), one track comprises a plurality of pieces of small-block record data (a plurality of pieces of small-block record data comprising continuous areas are separately present on an optical disk). These continuous pieces of information for music are present for each track and recorded and entered in a predetermined area of an MD as table-of-contents information. Hereafter, a predetermined area in which table-of-contents information is recorded is referred to as a UTOC (User Table of Contents) area.
It is possible to record not only the constitution information of each track but also additional information such as the year and date when data is recorded in each track, the name of an optical disk, and the name of a track in the UTOC area.
However, the timing for recording the table-of-contents information (linking information) of a track to be recorded in the UTOC area is not decided before recording of the recorded track is finished. This is because the amount of time that is recorded in the recorded track is unknown and thereby the end point of the track cannot be decided.
Therefore, hitherto, the table-of-contents information of the track of a recorded piece of music is recorded in the UTOC area when a recording-stop command key provided on an optical disk recorder (such as an MD) is pressed. However, when the power supply of the optical disk recorder is turned off due to outage while data is being recorded in the track, the information recorded in the track cannot be reproduced later because the table-of-contents information of the track record data is not recorded in the UTOC area of the MD.
This is because a signal for recording a piece of music in a track is recorded in a user's recording area but the entire information for controlling the area is saved in the UTOC area. An actual recording signal is completely separated from the table-of-contents information serving as control information. Therefore, it is impossible to reproduce the table-of-contents information of a track, that is, the block record data recorded in the track Just before the power supply is turned off, because there is no way to know the information showing the position of the user's recording area in which the block record data is present.
In this case, only one track fails in reproducing data. If the power supply is turned off while continuously recording block record data in a plurality of tracks (a piece of music) by recording data in the tracks and simultaneously incrementing them (increase of one track) or before recording table-of-contents information, the tracks in which the table-of-contents information is not recorded also fail in reproducing data. Therefore, problems occur that the entire time used to record the block record data in tracks comes to nothing and the recorder results in an apparatus having bad usage conditions.